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1.
In the present study, we have investigated the conditions influencing encystment and excystment in the dinoflagellate Gyrodinium instriatum under laboratory conditions. We incubated G. instriatum in modified whole SWM-3 culture medium and in versions of modified SWM-3 from which NO3 −, PO4 3−, NO3 − + PO4 3−, or Si had been omitted and observed encystment. Percentage encystment was high in the media without N and without P, while the percentage encystment in the medium lacking both N and P was highest. Moreover, to investigate N or P concentration which induced the encystment, Gyrodinium instriatum was also incubated in media with different concentrations of inorganic N and P; the concentrations of NO2 − + NO3 − and PO4 3− were measured over time. The precursors of cysts appeared within 2 or 3 days of a decrease in NO2 − + NO3 − or PO4 3− concentration to values lower than 1 μM or 0.2 μM, respectively. When cysts produced in the laboratory were incubated, we observed excystment after 8–37 days, without a mandatory period of darkness or low temperature. We incubated cysts collected from nature at different temperatures or in the dark or light and observed excystments. Natural cysts excysted at temperatures from 10 to 30°C, in both light and dark, but excystment was delayed at low temperatures. These studies indicate that G. instriatum encysts in low N or P concentration and excysts over a wide temperature range, regardless of light conditions, after short dormancy periods.  相似文献   

2.
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3.
The seasonal abundance of the dominant dinoflagellate, Ceratium fusus, was investigated from January 2000 to December 2003 in a coastal region of Sagami Bay, Japan. The growth of this species was also examined under laboratory conditions. In Sagami Bay, C. fusus increased significantly from April to September, and decreased from November to February, though it was found at all times through out the observation period. C. fusus increased markedly in September 2001 and August 2003 after heavy rainfalls that produced pycnoclines. Rapid growth was observed over a salinity range of 24 to 30, with the highest specific rate of 0.59 d−1 measured under the following conditions: salinity 27, temperature 24°C, photon irradiance 600 μmol m−2s−1. The growth rate of C. fusus increased with increasing irradiance from 58 to 216 μmol m−2s−1, plateauing between 216 and 796 μmol m−2s−1 under all temperature and salinity treatments (except at a temperature of 12°C). Both field and laboratory experiments indicated that C. fusus has the ability to grow under wide ranges of water temperatures (14–28°C), salinities (20–34), and photon irradiance (50–800 μmol m−2s−1); it is also able to grow at low nutrient concentrations. This physiological flexibility ensures that populations persist when bloom conditions come to an end.  相似文献   

4.
We measured the ammonium excretion, phosphate excretion and respiration rates of the scyphomedusa Aurelia aurita from Ondo Strait, in the central part of the Inland Sea of Japan, at 28 and 20°C. The rates measured at 28°C were converted to those at 20°C using the Q10 values, i.e. 1.56, 1.57 and 2.80, for ammonium excretion, phosphate excretion and respiration rates, respectively. The composite relationships between metabolic rates and wet weight of a medusa (WW, g, range 11–1330 g) at 20°C were expressed by the following allometric equations. For ammonium excretion rate (N, μmoles N medusa−1d−1): N = 0.497WW 1.09, phosphate excretion rate (P, μmoles P medusa−1d−1): P = 0.453WW 0.84, and respiration rate (R, μmoles O2 medusa−1d−1): R = 96.9WW 1.06. Mean O:N ratios (i.e. atomic ratios of 16.9 and 11.0 at 28 and 20°C, respectively) indicated that the metabolism of A. aurita medusae was protein-dominated. These metabolic parameters enabled us to estimate the nitrogen and phosphorus regeneration rates of an A. aurita medusa population typical of early summer in the Ondo Strait (means of water temperature, medusa individual weight and population biomass: 20°C, 200 g WW and 50.8 g WW m−3, respectively). Regenerated nitrogen and phosphorus were equivalent to 10.0 and 21.6% of phytoplankton uptake rates, respectively, nearly twice that estimated for mesozooplankton, demonstrating that A. aurita medusae are key components of the plankton community, influencing the trophic and nutrient dynamics in the Ondo Strait during early summer.  相似文献   

5.
Studies of macrophytes in the coastal zone of the Artic Seas, including the White Sea, have shown the essential role of these algae in the activity of the coastal half-latitude ecosystems. In summer, during the macrophyte reproduction period, a great number of reproduction products are released into the water. For a short time, this considerably affects the ratio of the nanoplankton in the populations that inhibit the vast and shallow coastal areas. At different coastal sites in Chernorechenskaya Inlet, Kadalaksha Bay, during the period of intensive reproduction of Ascophyllum nodosum and Fucus vesiculosus, 42 plankton samples were collected in 2005. During this period the concentration of antherozoids in the water reached 55000 cells/ml (216 mg C/m3). The number of eggs was within the range of 0.05–0.7 cells/ml. The proportion of antherozoids in the total biomass of nanoplankton varied at different coastal sites from 0.37 to 99%, with a mean of 46% for the reproduction period of A. nodosum, and only 7% for the reproduction period of F. vesiculosus. As was shown by counts of F. vesiculosus female gametes in sedimentation traps, 1 m2 of the macrophyte bed (assuming 100% coverage) produces 18000–108000 eggs per day (0.33–2 mg C). The calculated flux of the reproductive material from the brown algae beds to the coastal water shows good agreement with the sample counts.  相似文献   

6.
The studies were performed from September 10 to 29 of 2007 in the Kara Sea in transects westward of the Yamal Peninsula, near the St. Anna Trough, in the Ob River’s estuary, and on the adjacent shelf. The concentration of chlorophyll a in the euphotic layer changed from 0.02 to 4.37 mg/m3, amounting on the average to 0.76 mg/m3. The primary production in the water column varied from 10.9 to 148.0 mg C/m2 per day (the mean was 56.9 mg C/m2 per day). It was shown that frontal zones divided the Kara Sea into distinct areas with different productivities. The maximum levels of the primary production were measured in the deep part of the Yamal transect (132.4 mg C/m2 per day) and the shallow Kara Sea shelf near the Ob River’s estuary (74.9 mg C/m2 per day). The characteristics of these regions were the low salinity of the surface water layer (19–25 psu) and the elevated silicon content (12.8–28.1 μg-atom Si/l), which is explainable by the river water inflow. The frontal zones of the Yamal Current in the Yamal and Ob transects displayed high values of the assimilation numbers, amounting to 2.32 and 1.49 mg C/mg of chlorophyll per h, respectively (the maximal for the studied regions).  相似文献   

7.
The mitochondrial DNA (mtDNA) control region was sequenced to examine the genetic variability and gene flow of juvenile Siganus spinus and S. guttatus. In total, 461 nucleotide sequences were obtained from 69 specimens of juvenile S. spinus from Okinawa Island and Ishigaki Island, in which 17 variable sites and 22 haplotypes were identified. Haplotype diversity (h) was high (0.9244 in Okinawa and 0.8984 in Ishigaki), whereas nucleotide diversity (π) was low (0.0063 in Okinawa and 0.0059 in Ishigaki). The two populations were not genetically distinct. Siganus guttatus, which do not form large schools at recruitment, in contrast S. spinus, were also analyzed by studying 152 individuals collected off Okinawa Island, Miyako Island, and Ishigaki Island. Of 476 nucleotide sequences, 50 were variable, and 42 haplotypes were identified. Genetic variability values were high (h = 0.8766 and π = 0.0151 in Okinawa; h = 0.9640 and π = 0.0192 in Miyako; h = 0.9161 and π = 0.0199 in Ishigaki). The Okinawa population was genetically isolated from the Miyako and Ishigaki populations. As a result, genetic diversity was high for each of these siganid populations despite their being target species for fisheries; however, the degree of inter-population gene flow was higher for S. spinus than S. guttatus, suggesting that these species exhibit different dispersal strategies.  相似文献   

8.
A numerical experiment using a three dimensional level model was performed to clarify the mechanism generating a strong coastal current, Kyucho, induced by the passage of Typhoon 0406 around the tip of the Tango Peninsula, Japan in June 2004. Wind stress accompanied by Typhoon 0406 was applied to the model ocean with realistic bottom topography and stratification condition. The model well reproduced the characteristics of Kyucho observed by Kumaki et al. (2005), i.e., the strong alongshore current with maximum velocity of 53 cm s−1 and its propagation along the peninsula with propagation speed of about 0.6 m s−1 one half-day after the typhoon’s passage. Coastal-trapped waves (CTW) accompanied by downwelling were induced along the northwest coast of the peninsula by the alongshore wind stress. The energy density flux due to the CTW flowed eastward along the coast, and indicated scattering of the CTW around the eastern coast of the peninsula. In addition, significant near-inertial internal gravity waves were also caused in the offshore region from the west of the Noto Peninsula to the north of the Tango Peninsula by the typhoon’s passage. The energy flux density of the near-inertial fluctuations flowed southward off the Fukui coast, and part of the energy flux was trapped on the tip of the Tango Peninsula, flowing with the coast on its right. It was found that the strong current, Kyucho, at the northeastern tip of the Tango Peninsula was generated by superposition of the near-inertial internal gravity waves and subinertial CTW.  相似文献   

9.
Down-core variations in illite, chlorite, smectite and kaolinite (the major clays) in two 14C-dated cores collected along the SW continental margin of India show that illite and chlorite have enhanced abundance during 20–17, 12.5, 11–9.5, and 5–4.8 ka b.p., whereas smectite accumulation is higher between 17 and 12.5, and after 9 ka b.p. The climate may have been predominantly arid at 17 (20–17), 12.5, 10.5 (11–9.5), and 4.8 ka b.p. The first three dates correspond to the last glacial maximum, Bolling-Allerod, and Younger Dryas events, respectively. The SW monsoon was variable between 17 and 15 ka b.p., and it was more stable and intense after the Younger Dryas until about 6 ka b.p. Received: 2 December 1999 / Revision accepted: 11 April 2000  相似文献   

10.
In our attempt to characterize the interaction of trophic coupling between Synechococcus and pigmented nanoflagellates (PNFs), successive size-fraction experiments were performed at a coastal station on the northeast coast of Taiwan from June, 2005 to January, 2006. By estimating the growth rate and grazing rate of Synechococcus in the presence of nanoflagellates of different sizes, we truncated the food web by removing organisms with different body sizes (<2 μm, <5 μm, <10 μm, and <20 μm). The growth rates of Synechococcus ranged from −0.016 to 0.051 h−1 during the experimental period, suggesting that temperature was a primary mechanism controlling Synechococcus growth. In addition to size and relative biomass of pigmented nanoflagellates and Synechococcus, it is suggested that community structures played an important role in trophic link. Furthermore, we conclude that the trophic cascading effect in the northeast coast of Taiwan includes: 1) high grazing rates at night in the warm season; 2) the Synechococcus biomass generally exceeds the grazing threshold (6 × 104 cells mL−1); and 3) the biomass ratio of <5 μm PNFs to >5 μm PNFs should be 1:1 to 2:1.  相似文献   

11.
To examine the possibility that outer membrane proteins (OMP) of Synechococcus sp. remain in seawater, we investigated the stability of OMPs in vitro and in situ. Some fractions prepared from Synechococcus sp. CSIRO-94 were treated with trypsin and proteinase K. Four tightly bound OMPs were separated from Synechococcus. We designated the two major OMPs of 52 kDa and 48 kDa as Omp52Sy and Omp48Sy, respectively. Degradation of the OMP in natural seawater was monitored in microcosms to which intact Synechococcus cells and outer membrane (OM) were added. Omp52Sy and Omp48Sy were the most stable against trypsin and proteinase K among the OMPs when they were embedded in the OM. However, in the microcosm experiment using intact cells, Omp52Sy and Omp48Sy were detected in the particulate fraction only during the first 4 days, after which they could not longer be detected. Omp52Sy and Omp48Sy were the most stable proteins among the Synechococcus OMPs in vitro, but they might be degraded in situ. This indicates that stability of Synechococcus porin differs depending on complex formation with other membrane molecules, which might cause different preservation of microbial membrane proteins in the dissolved protein pool in the ocean. This study suggests that Gram negative bacterial OM with thin peptidoglycan forms a lipid bilayer that proptects OMP, but Synechococcus OM with thick peptidoglycan cannot form a lipid bilayer. The incomplete bilayer might not be able to protect from protease attack in the natural environment.  相似文献   

12.
Vibrio parahaemolyticus is a common pathogenic bacterium in marine and estuarine waters. To investigate interactions between V. parahaemolyticus and co-occurring redtide dinoflagellates, we monitored the daily abundance of 5 common red tide dinoflagellates in laboratory culture; Amphidinium carterae, Cochlodinium ploykrikoides, Gymnodinium impudicum, Prorocentrum micans, and P. minimum. Additionally, we measured the ingestion rate of each dinoflagellate on V. parahaemolyticus as a function of prey concentration. Each of the dinoflagellates responded differently to the abundance of V. parahaemolyticus. The abundances of A. carterae and P. micans were not lowered by V. parahaemolyticus, whereas that of C. polykrikodes was lowered considerably. The harmful effect depended on bacterial concentration and incubation time. Most C. polykrikoides cells died after 1 hour incubation when the V. parahaemolyticus concentration was 1.4×107 cells ml−1, while cells died within 2 days of incubation when the bacterial concentration was 1.5×106 cells ml−1. With increasing V. parahaemolyticus concentration, ingestion rates of P. micans, P. minimum, and A. carterae on the prey increased, whereas that on C. polykrikoides decreased. The maximum or highest ingestion rates of P. micans, P. minimum, and A. carterae on V. parahaemolyticus were 55, 5, and 2 cells alga−1 h−1, respectively. The results of the present study suggest that V. parahaemolyticus can be both the killer and prey for some red tide dinoflagellates.  相似文献   

13.
We compared the genetic diversity of three dominant myctophid fishes in the North Pacific Ocean that have different diel vertical migration patterns on the basis of the nucleotide sequences of the mitochondrial gene for cytochrome b. No genetic structure was detected for each of these three species. The genetic diversity progressively increased for Diaphus theta, a diel migrant species showing clear diel vertical migration; Stenobrachius leucopsarus, a semi-diel migrant, in which only part of the population migrates vertically; S. nannochir, a non-diel migrant. All three species were suggested to have experienced a recent, sudden population expansion. Interspecific differences in genetic diversity might be attributable to differences in the degree of population size reduction during the glacial periods; this degree in turn corresponds to the energy demand of the fishes.  相似文献   

14.
The habitat quality of Chub mackerel (Scomber japonicus) in the East China Sea has been a subject of concern in the last 10 years due to large fluctuations in annual catches of this stock. For example, the Chinese light-purse seine fishery recorded 84000 tons in 1999 compared to 17000 tons in 2006. The fluctuations have been attributed to variability in habitat quality. The habitat suitability Index (HSI) has been widely used to describe fish habitat quality and in fishing ground forecasting. In this paper we use catch data and satellite derived environmental variables to determine habitat suitability indices for Chub mackerel during July to September in the East China Sea. More than 90% of the total catch was found to come from the areas with sea surface temperature of 28.0°–29.4°C, sea surface salinity of 33.6–34.2 psu, chlorophyll-a concentration of 0.15–0.50 mg/m3 and sea surface height anomaly of −0.1–1.1 m. Of the four conventional models of HSI, the Arithmetic Mean Model (AMM) was found to be most suitable according to Akaike Information Criterion analysis. Based on the estimation of AMM in 2004, the monthly HSIs in the waters of 123°–125°E and 27°30′–28°00′ N were more than 0.6 during July to September, which coincides with the catch distribution in the same time period. This implies that AMM can yield a reliable prediction of the Chub mackerel’s habitat in the East China Sea.  相似文献   

15.
The food habits of the dominant myctophid Stenobrachius leucopsarus were examined in the central basin of the Bering Sea in relation to oceanographic conditions, in summer 2002 and 2003 and spring 2006. S. leucopsarus exhibited an ontogenetic and seasonal dietary shift. In spring, small fish (≤40 mm) preyed mainly on Neocalanus flemingeri/plumchrus whereas large fish fed mainly on Neocalanus cristatus. In summer, small fish preyed mainly on Metridia pacifica whereas large fish fed mainly on euphausiids (Thysanoessa spp.). In the summer of 2003, when water temperature in the epipelagic layer (≤100 m) was warmer, reflecting the prevalence of the Alaskan Stream, small-sized S. leucopsarus showed a higher stomach content index, perhaps reflecting the greater abundance of M. pacifica. Thus, the present study shows that the physical variability in the epipelagic layer affects not only diets but also feeding performance of micronekton.  相似文献   

16.
The egg production rate (EPR) of Calanus sinicus was measured from March 2007 to April 2010 at three stations along the Korean coast of the Yellow Sea (in coastal waters off Saemangum, Yeongheungdo, and Asan Bay) to estimate in situ maximum egg production rate (MEPR) and to understand whether the females were limited in their growth or fecundity in the field. The mean EPR of C. sinicus at each sampling date ranged from 10.3–34.9 eggs female−1 d−1 (mean 23.4 eggs female−1 d−1), and the EPR of individual copepods ranged from 0–81 eggs female−1 d−1. The mean EPR was positively correlated with the body weight of female copepods. The MEPR at each sampling date ranged from 40–81 eggs female−1 d−1 (mean 50.4 eggs female−1 d−1). Over 84% of eggs spawned hatched successfully. The weight-specific growth rate (WSGR) ranged from 0.038–0.111 d−1 (mean 0.082 d−1), indicating that 3.8–11.1% of the carbon in an adult female was produced daily as female growth. The WSGR was negatively correlated with water temperature. The ratio of mean EPR to observed mean MEPR ranged from 20–70% (mean 46%), indicating that ∼54% of a female’s growth might be limited in the field. We suggest that the ratio of observed EPR to mean MEPR of copepod can be applied to understand how the copepod responds to environmental changes, as well as EPR and hatching success.  相似文献   

17.
The optimum conditions were selected for the chromatographic separation of model mixtures of C12–C40 n-alkanes. For one of the samples of hydrothermal deposits, the extraction conditions of the hydrocarbons were studied and a sample preparation procedure was selected. A procedure is proposed to determine the n-alkanes in samples of hydrothermal deposits by means of gas chromatography-mass spectrometry (GC-MS). The detection limit for the n-alkanes amounted to 3 × 10−9 to 10−8% depending on the components. On the basis of the procedure proposed, the composition of the n-alkanes was studied in the samples of hydrothermal deposits collected at the Mid-Atlantic Ridge (the Broken Spur, Lost City, and Rainbow fields). The analysis performed showed that the samples treated contained C14-C35 n-alkanes. The concentrations of the n-alkanes considered were rather low and varied from 0.002 to 0.038 μg/g. Hypotheses concerning the genesis of the n-alkanes identified were formed.  相似文献   

18.
To date no analytical solution of the pile ultimate lateral capacity for the general c–φ soil has been obtained. In the present study, a new dimensionless embedded ratio was proposed and the analytical solutions of ultimate lateral capacity and rotation center of rigid pile in c–φ soils were obtained. The results showed that both the dimensionless ultimate lateral capacity and dimensionless rotation center were the univariate functions of the embedded ratio. Also, the ultimate lateral capacity in the c–φ soil was the combination of the ultimate lateral capacity (f c ) in the clay, and the ultimate lateral capacity (f φ ) in the sand. Therefore, the Broms chart for clay, solution for clay (φ=0) put forward by Poulos and Davis, solution for sand (c=0) obtained by Petrasovits and Awad, and Kondner’s ultimate bending moment were all proven to be the special cases of the general solution in the present study. A comparison of the field and laboratory tests in 93 cases showed that the average ratios of the theoretical values to the experimental value ranged from 0.85 to 1.15. Also, the theoretical values displayed a good agreement with the test values.  相似文献   

19.
Fugacity of CO2 (fCO2), temperature, salinity, nutrients, and chlorophyll-a were measured in the surface waters of southwestern East Sea/Japan Sea in July 2005. Surface waters were divided into three waters based on hydrographic characteristics: the water with moderate sea surface temperature (SST) and high sea surface salinity (SSS) located east of the front (East water); the water with high SST and moderate SSS located west of the front (West water); and the water with low SST and SSS located in the middle part of the study area (Middle water). High fCO2 larger than 420 μatm were found in the West water. In the Middle water, CO2 was undersaturated with respect to the atmosphere, with values between 246 and 380 μatm. Moderate fCO2 values ranging from 370 to 420 μatm were observed in the East water. For the East and West waters, estimates of temperature dependency of fCO2 (12.6 and 15.1 μatm °C−1, respectively) were rather similar to a theoretical value, indicating that SST is likely to be a major factor controlling the surface fCO2 distribution in these two regions. In the Middle water, however, the estimated temperature dependence was somewhat lower than the theoretical value, and relatively high concentrations of surface chlorophyll-a coincided with the low surface fCO2, implying that biological uptake may considerably affect the fCO2 distribution. The net sea-to-air CO2 flux of the study area was estimated to be 0.30±4.81 mmol m−2 day−1 in summer, 2005.  相似文献   

20.
Seafloor pockmarks and subsurface chimney structures are common on the Norwegian continental margin north of the Storegga Slide scar. Such features are generally inferred to be associated with fluid expulsion, and imply overpressures in the subsurface. Six long gravity and piston cores taken from the interior of three pockmarks were compared with four other cores taken from the same area but outside the pockmarks, in order to elucidate the origins and stratigraphy of these features and their possible association with the Storegga Slide event. Sulfate gradients in cores from within pockmarks are less steep than those in cores from outside the pockmarks, which indicates that the flux of methane to the seafloor is presently smaller within the pockmarks than in the adjacent undisturbed sediments. This suggests that these subsurface chimneys are not fluid flow conduits lined with gas hydrate. Methane-derived authigenic carbonates and Bathymodiolus shells obtained from a pockmark at >6.3 m below the seafloor indicate that methane was previously available to support a chemosynthetic community within the pockmark. AMS 14C measurements of planktonic Foraminifera overlying and interlayered with the shell-bearing sediment indicate that methane was present on the seafloor within the pockmark prior to 14 ka 14C years b.p., i.e., well before the last major Storegga Slide event (7.2 ka 14C years b.p., or 8.2 ka calendar years b.p.). These observations provide evidence that overpressured fluids existed within the continental margin sediments off Norway during the last major advance of Pleistocene glaciation.  相似文献   

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